Computer systems requiring high-availability and fault tolerance often employ redundant power architectures that allow the systems to continue to run even if the input power to a power supply component is interrupted, or if a power supply component fails. These redundant power architectures include the use of a plurality of power supplies (typically isolated AC/DC Power supplies, but also isolated and non-isolated DC/DC Power supplies) that produce one or more output power rails which power the system circuitry. The use of more than one power supply or more than one output power rail allows the system to receive power from the redundant power supply or redundant power rail in the event the primary power supply or primary power rail is unable to provide power. The plurality of power supplies in such an architecture often contain electronic components on their outputs that allow the power supplies to source current to the system loads, but prevent current from flowing in the reverse direction from the load side back into the power supply. Preventing the reverse current flow is critical in redundant architectures so that a failed power supply does not load down the system bus. These “Fault-Isolation” devices that prevent reverse current flow into the power supply are commonly referred to in the art as “OR'ing” devices, as they allow the load to be powered from one power supply “OR” the other “redundant” power supplies.
Conventional architectures may use a diode or a Mosfet to provide the “OR'ing” function. Use of a semiconductor diode for this function provides simplicity from a design approach, but may suffer in comparison to a Mosfet with low source-drain resistance (“RDS”) from an electrical efficiency approach. Regardless of the type of “OR'ing” device used, the “OR'ing” function is one important design element that must work properly in order to provide fault tolerant power to the system. Another design requirement in a redundant power architecture is to have redundant power supplies that are capable of supporting the requisite system load current in the event of a failure in one of the other power supplies. For example, in a system requiring “x” Watts with N+1 redundancy, the power architecture could employ two power supplies, each capable of independently providing “x” Watts of power. Having the second power supply is of little use if it is not properly sized, or if it is not functioning properly so that it is able carry the full system load.
Designing power supplies with “OR'ing” functionality, and adequately sizing those supplies to support the worst-case system load is relatively straightforward. However, ensuring that a particular power supply has (a) a properly functioning “OR'ing” feature, and (b) can properly support the requisite load when called upon, is problematic once the units are in operation in a system. While both of these functions can be, and typically are, initially tested by the power supply manufacturer prior to being installed in a computer system, the system in which they are installed can become vulnerable to a latent (hidden) defect in those features, if the defect occurs during or after the power supply installation in the system. For example, a defect in the “OR'ing” circuit such that the “OR'ing” device is “open” or “shorted” may go undetected until that power supply or its redundant power supply fails. At that point, the “open” or “shorted” “OR'ing” device can result in the interruption of power to the system. Similarly, a redundant power supply designed to supply “x” Watts that, due to some latent defect, can not support a full load of “x” Watts, would cause an interruption in power to the system if the peer supply experienced a failure. Interruption of power to the system (as described in the examples above) as a result of a latent defect in the power architecture is problematic to systems requiring high availability.
Currently, there is no method or system for testing for these defects in power supplies that are in operation in the field.
Another potential shortcoming in redundant power architectures is that sizing of the power supplies can be a challenge, as the total system loads may vary depending on the customer's desired system configuration. As a result, system designers often must oversize the power supply, from an output power rating perspective, to be capable of supporting the worst case system load. The consequence of this is that the power supply, when installed in a minimally configured system, may be running at very light loads when the peer power supply is not faulted. Since power supplies intended for use in redundant architectures are conventionally designed to have their optimal (greatest) electrical efficiency at or near fifty percent load, they will often suffer, somewhat, from a reduced efficiency when running at full or light load conditions. As a result, the power supplies used in conventional redundant power architectures may not be running at their optimum electrical efficiency, depending on the amount of load being demanded from them by the system.